Although the mobo supports this resolution, the monitor is not recognized, and the system gives me a 1600x1200 display stretched to fill the monitor. The System Settings -> Displays shows the screen as Unknown, Detect Displays does nothing, and 1600x1200 is the max resolution.

I used xrandr to create a 1920x1200 mode, and add it to the display called "default", and aside from a bunch of "Failed to get size of gamma for output default" errors, it does indeed add that mode to the choices in Displays. However, when I select that new mode, it complains "required virtual size does not fit available size", since the max is still 1600x1200. It doesn't say what exactly is enforcing that limit.

After a lot of Googling, I found a couple of recommendations that I create an xorg.conf file (there was none), and put something like this into it: